ATM-based distributed virtual tandem switching systme

ABSTRACT

An Asynchronous Transfer Mode (ATM)-based distributed virtual tandem switching system is provided in which a network of ATM-based devices is combined to create a distributed virtual tandem switch. The system includes an ATM switching network that dynamically sets up individual switched virtual connections. The system also includes a trunk interworking function (T-IWF) device and a centralized control and signaling interworking function (CS-IWF) device. The trunk interworking function device converts end office voice trunks from TDM channels to ATM cells by employing a structured circuit emulation service. The centralized control and signaling interworking function device performs call control functions and interfaces narrowband signaling and broadband signaling for call processing and control within the ATM switching network. Consequently, the ATM based distributed virtual tandem switching system replaces a standard tandem switch in the PSTN.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/024,182, filed Dec. 21, 2001, which is a continuation of U.S. patentapplication Ser. No. 09/666,839, filed Sep. 21, 2000, which is now U.S.Pat. No. 6,345,048, which is a continuation of U.S. patent applicationSer. No. 09/287,092, filed Apr. 7, 1999, which is now U.S. Pat. No.6,169,735, which claims the benefit of U.S. Provisional PatentApplication No. 60/083,640 filed on Apr. 30, 1998, entitled “ATM-BasedDistributed Virtual Tandem Switching System” to ALLEN et al., thedisclosures of all of which are expressly incorporated herein byreference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a telecommunications architecture. Moreparticularly, the present invention relates to tandem switching systemsfor use within a public switched telephone network (PSTN). The presentinvention enables voice trunking over an asynchronous transfer mode(ATM) network by replacing tandem switches with a distributed virtualtandem switching system that includes a high speed ATM network. Thereplacement is virtual because as far as the end offices are concerned,the ATM-based distributed virtual tandem switching system isfunctionally equivalent to the traditional time division multiplexed(TDM) tandem switching system.

2. Background Information

Within the public switched telephone network (PSTN), an originatingcaller communicates with a destination by establishing a connectionbetween an end office serving the originating caller and an end officeserving the destination. FIG. 1 shows the architecture of the currentPSTN. In today's PSTN, end office switches 10 are connected to eachother via tandem trunk groups 12, direct trunk groups 14, or both tandemtrunk groups 12 and direct trunk groups 14. Each trunk within a trunkgroup is typically a digital service level 0 (DS0) (i.e., 64 kilobitsper second) communication line that transmits between the end offices 10in a time division multiplexed (TDM) manner. When an end office utilizesa direct trunk group 14, the connection between the end offices 10 iswithout any intermediaries. When an end/central office 10 utilizes atandem trunk group 12, the connection between end offices 10 is via atandem switch 16.

The tandem switch or office 16 is an intermediate switch or connection,between an originating telephone call location and the final destinationof the call, which passes the call along. Tandem switches are oftenutilized to handle overflow calls. That is, when all paths are busy on aprimary route, e.g., the direct interoffice trunk group 14 between theoriginating and destination end offices 10, alternative routes throughthe tandem switch 16 handle the overflow call volume. The tandem switch16 can also function as a physical path to non-directly-connectedoffices in addition to functioning as an overflow path for directlyconnected offices. If the overflow route through the tandem switch 16becomes full, an alternate final route may be provided. The alternatefinal route is via another end office 10, thus employing two interofficetrunk groups 14.

Signaling is needed within the PSTN to establish a connection (i.e.,setup a telephone call) between a calling party and a destination. Thesignaling enables line acquisition and sets up call routing, in additionto performing other functions. The signaling can be transmitted througha channel common with the voice data (in-band signaling) or can betransmitted through a dedicated channel (out of band signaling). Thedominant signaling protocol currently in use today is transmitted viathe dedicated channel and is called Signaling System 7 (SS7).

A conventional connection setup between two end offices 20, 22 in atandem network is now described with reference to FIGS. 2 and 3. When acalling party 19 (e.g., 235-1111) dials a telephone number (e.g.,676-2222), the originating central office 20 interprets the dialeddigits and routes the call to either a direct interoffice trunk group 14between end offices 20, 22 or a pair of tandem office trunk groups 12and the corresponding tandem switch 16 between end offices 20, 22.Assuming the pair of tandem office trunk groups 12 and the correspondingtandem switch 16 is utilized, a trunk from each of the trunk groups 12needs to be selected and reserved by signaling within the SS7 network.Thus, necessary information is transmitted from the originating endoffice 20 to its associated signaling transfer point 18. Although only asingle signaling transfer point is shown in the figures, a networktypically includes many signaling transfer points. Thus, each signalingtransfer point 18 transfers signals from one signaling link to anothersignaling link in the SS7 network that transports SS7 messages.

The transmitted information is in the form of an ISUP (ISDN user part)message. It contains a unique point code, which uniquely identifies eachend office, corresponding to the originating end office (originatingpoint code (OPC)) and the destination (destination point code (DPC)).Because the message must first go to the tandem office 16, the ISUPmessage contains the destination point code of the tandem office. Themessage also contains a circuit identification code (CIC) thatcorresponds to the physical circuit that will be employed to transportthe data. Thus, interoffice trunks are identified by originating pointcode (OPC), destination point code (DPC), and circuit identificationcode (CIC).

As shown in the example illustrated in FIG. 3, initially an ISUP messageis sent containing a DPC equal to 246 1 2, an OPC equal to 246 1 1, anda CIC equal to 22. Consequently, a circuit will be setup between theoriginating end office 20 and the tandem office 16. The tandem switch 16receives the SS7 message and determines from the called number, which isembedded in the protocol, where to route the call, i.e., the appropriatedestination end office 22. Then, via the SS7 network, the call is setupbetween the tandem switch 16 and the appropriate terminating office 22in a similar manner. Thus, because the tandem office 16 needs totransport the data to the destination end office 22, the tandem office16 sends an ISUP message to the signaling transfer point 18, includingthe destination end office=s destination point code, i.e., 246 1 3, thetandem office's origination point code, i.e., 246 1 2, and the circuitidentification code corresponding to the circuit between the tandemoffice 16 and the destination office 20, e.g., circuit 7. After thisISUP message is sent to the signaling transfer point 18, the signalingtransfer point 18 forwards the ISUP message to the destination endoffice 22 in order to setup the connection between the tandem office 16and the destination office 22, thus reserving the circuit. Theterminating central office switch 22 receives the SS7 message anddetermines where to terminate the call by interpreting the called numberembedded in the protocol.

A call flow scenario is now described with reference to FIG. 2. A caller19 dials the telephone number of a destination 23. The first end office20 (end office A) collects the digits of the called number and checksrouting tables to determine to which end office 22 the dialed telephonenumber belongs. Then the originating end office 20 finds a direct trunkgroup 14 between itself and the end office owning the dialed telephonenumber. Subsequently, the originating end office finds an idle trunkwithin the trunk group 14. The originating end office 20 selects andreserves the idle trunk of the trunk group 14 and initiates an SS7 IAM(initial address message) message containing the following: signalingtransfer point routing address of the destination end office; thecalling telephone number; the called telephone number, and the trunk ID(CIC) for the selected trunk of the trunk group.

The signaling transfer point 18 receives the IAM message and forwards itto the destination end office 22. The destination end office 22 thenreceives the IAM message and uses the CIC information to reserve theselected trunk within the trunk group 14. The destination end office 20(end office B) then checks the called telephone number 23 for on-hookand feature support and holds the line, assuming the dialed telephonenumber is on hook. The destination end office 22 then applies a ring tothe line and ring tone to the selected trunk in the trunk group 14.Next, the destination end office 22 connects the dialed telephone numberline to the selected trunk in the trunk group 14, initiates an SS7 ACM(Address Complete Message) message and forwards it to the signalingtransfer point 18.

The signaling transfer point receives the ACM message and forwards it tothe originating end office 20 that receives the ACM message. Theoriginating end office 20 then connects the calling telephone numberline to the selected trunk. Consequently, the caller of the callingnumber hears a ring tone and the called party at the called telephonenumber picks up the phone. The destination end office 22 detects the offhook on the called telephone number 23 and removes the ring tone. Thedestination end office 22 then initiates an SS7 ANM (answer) message tothe signaling transfer point 18. The signaling transfer point 18receives the ANM message and forwards it to the originating end office20. The originating end office 20 receives the ANM message and startsnecessary billing measurement. Ultimately, the caller speaks with thecalled party.

Another call flow scenario according to the prior art is now describedwith reference to FIG. 2. Initially, a caller, e.g., 235-1111 dials adestination, e.g., 676-2222. The originating end office 20 (end officeA) collects digits of the called number and checks routing tables todetermine which end office handles 676. The originating end office 20finds that 676 belongs to a destination end office 22 (end office B).End office A then locates a direct trunk group 14 to end office B.Assume in this example that no idle trunk exist within the direct trunkgroup 14. Thus, end office A chooses and reserves a first tandem trunkgroup 12, and a selected trunk from the first reserved trunk group 12.Subsequently, end office A initiates an SS7 IAM message containing thefollowing: signaling transfer point routing address of the tandem;calling telephone number; called telephone number; and trunkidentification (CIC) for the selected trunk of the first reserved trunkgroup 12.

The signaling transfer point 18 receives the IAM message and forward itto the tandem switch 16. The tandem office 16 receives the IAM messageand utilizes the CIC information to reserve the selected trunk of thefirst reserved trunk group 12. The tandem office 16 then checks arouting table to determine the destination and reserves a selected trunkof a second trunk group 12, which connects to the destination.Subsequently, the tandem 16 initiates an SS7 IAM message to thesignaling transfer point 18 with the following information: signalingtransfer point routing address of end office B; calling telephonenumber; called telephone number; and trunk identification (CIC) for theselected trunk of the second trunk group 12.

The signaling transfer point 18 receives the IAM message and forwards itto end office B. End office B receives the IAM message and utilizes theCIC information to reserve the selected trunk of the second trunk group12. End office B checks whether the called telephone number is on-hookand holds the line, assuming that 676-2222 is on-hook. End office Bapplies ringing to the line and a ring tone to the selected trunk of thesecond trunk group 12. End office B then connects the line to theselected trunk of the second trunk group 12 and initiates an SS7 ACMmessage to the signaling transfer point 18.

The signaling transfer point 18 receives the ACM message and forward itto the tandem switch 16. The tandem switch 16 receives the ACM messagefrom the signaling transfer point 18 and consequently, the tandem switchinitiates an ACM message to the signaling transfer point 18.

The signaling transfer point 18 receives the ACM message and forwards itto end office A. End office A receives the ACM message and connects235-1111 to the selected trunk of the first reserved trunk group 12.Next, the caller at 235-1111 hears a ring tone and the called party at676-2222 picks up the phone.

Consequently, end office B detects an off-hook on 676-2222. Accordingly,end office B removes the ring tone and initiates an ANM message to thesignaling transfer point 18. The signaling transfer point 18 receivesthe ANM message and forwards it to the tandem switch 16. The tandemswitch 16 receives the ANM message from the signaling transfer point 18and the tandem switch 16 initiates an ANM message to the signalingtransfer point 18.

The signaling transfer point 18 receives the ANM message from the tandemswitch and forwards it to end office A. End office A receives the ANMmessage from the signaling transfer point 18 and starts necessarybilling measurement. Finally, the calling party at 235-1111 talks to thecalled party at 676-2222.

The current system has disadvantages. In order to minimize overflow callvolume, the size of a trunk group needs to be forecast so that the trunkgroup can handle the expected call volume. Then, appropriately sizedtrunk groups are preprovisioned, each having a dedicated bandwidth. Theprocess of forecasting and preprovisioning is expensive. Moreover, thecurrent trunking architecture requires a large number of small trunkgroups to link end offices because of the large number of end officesthat each end office must connect with. This form of trunking leads toinefficiencies due to the relatively small size of a significant numberof the trunk groups. That is, the small size reduces the call carryingcapacity per trunk and therefore requires a larger percentage ofoverflow trunking. In addition, the large number of trunk groupsrequires huge investments in hardware and software for systems that keeptrack of individual interoffice trunks. Further, the trunk forecastingand provisioning is necessary for thousands of individual trunk groups.

The ATM Forum's VTOA Group has attempted to solve the problemsassociated with voice trunking over ATM. The VTOA Group developed aspecification for carrying voice over ATM in a private networkenvironment. For example, see ATM Forum Technical Committee, “CircuitEmulation Service Interoperability Specification Version 2.0” (January1997). That specification allows private businesses to employ an ATMnetwork to establish voice channels across the ATM network using aprotocol, such as private network-network interface (PNNI), whichfacilitates moving cells from one point in the ATM network to anotherpoint in the ATM network. However, the specification is limited toapplication within a private environment, which is not appropriate forapplications in the PSTN. That is, interaction is not supported withsystems that include out-of-band signaling, e.g., Signaling System 7(SS7), which is essential to supporting capabilities such as an advancedintelligent network (AIN).

Within these private networks, the signaling is typically in-bandsignaling. Thus, no interface with an out-of-band signaling networkwould be required. Moreover, if a calling party within the privatenetwork would like to contact someone outside of the private network,the calling party must communicate over the normal PSTN, thus leavingthe scope of the VTOA Group's system.

U.S. Pat. No. 5,483,527 addresses voice trunking within the PSTN. Thepatent discloses a system that interposes an ATM network between twocentral offices. Signaling is sent from the central office via asignaling transfer point (STP) to the ATM switch. Within each ATMswitch, a processing system is provided for interfacing the ATM switchwith the STP. Thus, the ATM switches are modified to be able tocommunicate with the signaling transfer point, which is a very expensiveprocess. Furthermore, due to the interface being provided within eachATM switch, the path across the ATM network is established relativelyslowly. Finally, the distributed placement of the interface between thesignaling transfer points and the ATM network has its own disadvantages.

Glossary of Acronyms

AAL ATM Adaptation Layer

ACM Address Complete Message

ADPCM Adaptive Differential Pulse Code Modulation

ADSL Asymmetric Digital Subscriber Line

AIN Advanced Intelligent Network

ANM Answer Message

ANSI American National Standards Institute

ATM Asynchronous Transfer Mode

B-ISUP Broadband ISDN User Part

CAS Channel Associated Signaling

CBR Constant Bit Rate

CCS Common Channel Signaling

CES Circuit Emulation Service

CIC Circuit Identification Code

CS-IWF Control and Signaling Interworking Function

DPC Destination Point Code

DS0 Digital Signal Level 0 (64 Kbps digital signal format)

DS1 Digital Signal Level 1 (1.544 Mbps digital signal format)

IAM Initial Address Message

IP Internet Protocol

ISDN Integrated Service Digital Network

ISUP ISDN User Part

ITU-T International Telecommunications Union-Telecommunications

IWF Interworking Function

IXC Interexchange Carrier

OAM&P Operations, Administration, Maintenance, and Provisioning

OC12 Optical Carrier level 12 signal (622 Mbps)

OC3 Optical Carrier level 3 signal (155 Mbps)

OPC Originating Point Code

PCM Pulse Code Modulation

PNNI Private Network-Network Interface

POTS Plain Old Telephone Service

PSTN Public Switched Telephone Network

SS7 Signaling System 7

SSP Service Switching Point

STP Signal Transfer Point

SVC Switched Virtual Connection

TDM Time Division Multiplexing

T-IWF Trunk Interworking Function

UNI User-to-Network Interface

VTOA Voice and Telephony over ATM

SUMMARY OF THE INVENTION

In view of the foregoing, the present invention is directed to providinga replacement for the current trunking system operating between endoffices, as well as between end offices and an interexchange carriernetwork.

Accordingly, an Asynchronous Transfer Mode (ATM) based distributedvirtual tandem switching system is provided. The system comprises an ATMswitching network, a trunk interworking function (T-IWF) device, and acentralized control and signaling interworking function (CS-IWF) device.The trunk interworking function (T-IWF) device is adapted to receive endoffice voice trunks from time division multiplexed (TDM) channels andconvert the trunks to ATM cells. The centralized control and signalinginterworking function (CS-IWF) device performs call control functionsand is adapted to interface narrowband and broadband signaling for callprocessing and control within the ATM switching network. Thus, the ATMbased distributed virtual tandem switching system replaces a standardtandem switch.

According to a preferred embodiment, the T-IWF includes a circuitemulation service. Further, the T-IWF can include ATM adaptation layer 1(AAL1). Alternatively, the T-IWF adapts circuit traffic to ATM cellsutilizing ATM adaptation layer 2 (AAL2). If AAL2 is employed, silencesuppression and/or voice compression can be supported.

According to a preferred embodiment, each voice trunk is setupdynamically as an individual switched virtual connection in the ATMswitching network. Moreover, the T-IWF and the end office switch arepositioned at the same location.

According to a preferred embodiment, the narrowband signaling is SS7signaling. In addition, the broadband signaling is preferably PNNI,B-ISUP, and/or UNI.

A method is provided for transporting voice from an originating locationto a destination across an Asynchronous Transfer Mode (ATM) network. Themethod includes transmitting the voice from the originating location toan originating trunk that leaves an end office switch; converting theoriginating trunk to ATM cells; and interfacing between narrowband andbroadband signaling for call processing and control within the ATMnetwork. Moreover, the method includes transmitting the voice within theATM cells across the ATM network utilizing the broadband signaling;converting the ATM cells to a destination trunk; and transmitting thevoice from the destination trunk to the destination.

According to a preferred embodiment, the transporting is enabled byemulating a circuit by employing a circuit emulation service. Further,the voice may be converted to ATM cells utilizing ATM adaptation layer 1(AAL1). Alternatively, the voice may be converted to ATM cells utilizingATM adaptation layer 2 (AAL2). If AAL2 is selected, silence suppressionand/or voice compression is employed.

According to a preferred embodiment, each voice trunk is setupdynamically as an individual switched virtual connection in the ATMnetwork. Moreover, converting the originating trunk to ATM cells occursin the T-IWF within an originating end office and converting the ATMcells to a destination trunk occurs in the T-IWF within a destinationend office.

According to a preferred embodiment, the narrowband signaling is SS7signaling. In addition, the broadband signaling preferably is PNNI,B-ISUP, and/or UNI.

According to a preferred embodiment, an Asynchronous Transfer Mode(ATM)-based distributed virtual tandem switching system is provided inwhich a network of ATM-based devices is combined to create a distributedvirtual tandem switch. The system includes an ATM switching networksetup dynamically with individual switched circuits. The system alsoincludes a trunk interworking function device and a centralized controland signaling interworking device. The trunk interworking functionconverts end office trunks from TDM channels to ATM cells by employing acircuit emulation service. The centralized control and signalinginterworking function device performs call control functions andinterfaces narrowband signaling and broadband signaling for callprocessing and control within the ATM switching network. Consequently,the ATM based distributed virtual tandem switching system replaces astandard tandem switch.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described in the detailed descriptionthat follows, by reference to the noted plurality of drawings by way ofnon-limiting examples of preferred embodiments of the present invention,in which like reference numerals represent similar parts throughoutseveral views of the drawings, and in which:

FIG. 1 shows a prior art system for communicating between end offices;

FIG. 2 shows a known trunk group architecture;

FIG. 3 shows a known dedicated out-of-band signaling network associatedwith a tandem network and exemplary ISUP messages;

FIG. 4 shows an exemplary architecture of an ATM-based distributedvirtual tandem switching system according to an aspect of the presentinvention;

FIG. 5 shows an exemplary architecture of an ATM-based distributedvirtual tandem switching system including an out-of-band signalingnetwork, according to an aspect of the present invention;

FIG. 6 shows an exemplary trunk group architecture according to anaspect of the present invention; and

FIG. 7 shows an alternative architecture for an ATM-based distributedvirtual tandem switching system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An ATM-based distributed virtual tandem switching system is provided forreplacing standard tandem switches and facilitating the reduction ofnecessary trunk groups without decreasing call processing volume.

Referring now to FIG. 4, the ATM-based distributed virtual tandemswitching system according to the present invention is described.Originating end office 20 and terminating end office 22 are similar tothe central offices 10 shown in FIG. 1. The end offices 10 are typicallyClass 5 switches such as the 5ESS available from Lucent Technologies,Inc. of Murray Hill, N.J., or the DMS100 available from Northern TelecomLtd. (Nortel Networks) of Canada. However, any other Class 5 end officeswitch may be substituted for the Nortel and Lucent switches. Also shownis a signaling transfer point (STP) 18. The signaling transfer point 18is well known in the art and may be provided, for example, by Alcatel ofFrance. The signaling transfer point 18 communicates with the endoffices 20, 22 via SS7 signaling as described above. An asynchronoustransfer mode (ATM) switching network 26 is also provided. The ATMswitches within the network can be provided by vendors such as, but notlimited to, Lucent, Cisco Systems, Inc. of San Jose, Calif., or Nortel.

A trunk interworking function (T-IWF) device 28 is also provided.Although described as a device, the T-IWF 28 can be multiple devices orany combination of hardware and software. The T-IWF 28 converts endoffice 20, 22 voice trunks from TDM channels to ATM cells. Moreparticularly, the T-IWF 28 segments the 64 Kbps bearer channels into ATMcells in one direction and reassembles ATM cells in the 64 Kbps channelsin the other direction. Preferably, the T-IWFs 28 are distributedthroughout the PSTN with a T-IWF 28 corresponding to each end office 20,22. An exemplary T-IWF 28 is a Succession Multiservice Gateway (SMG)4000, provided by Nortel. However, any other T-IWF 28 may be employed.

The ATM-based distributed network also requires a centralized controland signaling interworking function (CS-IWF) device 30. Althoughdescribed as a device, the CS-IWF 30 can be multiple devices or anycombination of hardware and software. The CS-IWF 30 performs necessarycall control functions as well as conversion between a narrowbandsignaling, e.g., Signaling System 7 (SS7), protocol, and a broadbandsignaling protocol for call processing and control within the ATMnetwork. Preferably, a single CS-IWF 30 serves all the T-IWFs 28 in ametropolitan area. An exemplary CS-IWF 30 is a Succession Call Server(SCS), provided by Nortel. However, any other CS-IWF 30 may be employed.

The T-IWFs 28, the CS-IWF 30, the ATM switching network 26, and theinterconnecting links together comprise the ATM-based distributedvirtual tandem switching system. The system is distributed because thetandem functions are carried out in part by the T-IWFs 28 that arelocated near the end offices 20, 22 in a distributed manner. The systemis virtual because as far as the end offices 20, 22 are concerned, theATM-based distributed virtual tandem switching system is functionallyequivalent to the traditional time division multiplexed (TDM) tandemswitching system 16. Thus, end offices 20, 22 require only slightconfiguration changes in order to utilize the present invention. Thevirtual aspect also refers to the fact that the individual trunks are nolonger DS0 time slots that need to be statistically provisioned. Rather,the trunks are realized through dynamically established ATM switchedvirtual connections.

Deployment of the ATM-based distributed virtual tandem switching systemallows an end office 20, 22 to handle normal call volumes while havingonly one or a few large trunk groups connecting to the ATM switchingnetwork, thus eliminating the need to provision separate trunk groups todifferent destination end offices. In addition, the total trunkingbandwidth is shared by traffic to all destinations because ATM virtualconnections are provisioned on demand by signaling. Consequently,bandwidth is not dedicated to any TDM voice channels betweenpredetermined locations, but rather is dynamically shared.

According to a preferred embodiment, end offices 20, 22 have a singlelarge trunk group that connects with the virtual tandem switch, althoughexceptions may exist where more than one trunk group is needed, forexample, if an end office limits the number of members in a trunk groupconnected to the end office. Consequently, the direct interoffice trunks14 between end offices 10 (shown in FIG. 1) are eliminated.

Thus, the present invention reduces the total number of trunks needed inan end office 20, 22, improves trunk utilization, and reduces oreliminates the task of trunk forecasting and provisioning. Furthermore,growth in trunking needs by the end office switches 20, 22 can be moreeasily met because the virtual tandem switching system of the presentinvention allows scalability supported by ATM networks. The scalabilityis achieved because of the ATM network's greater bandwidth and the ATMnetwork's statistical multiplexing, which more efficiently utilizesexisting bandwidth. The trunk interworking function T-IWF 28 is a devicethat is preferably located in the same structure or building that houseseach end office switch 20, 22. More particularly, the T-IWF 28 isimplemented with one or more physical devices that are external to theswitch 20, 22, but within the same end office that houses thecorresponding switch(es) 20, 22. The reason for the co-location is thatthe sooner the TDM trunks are converted to ATM, the earlier theadvantages of ATM statistical multiplexing gains are enjoyed. Becausethe T-IWF 28 is physically located in the central office 20, 22, theT-IWF 28 must meet the central office environmental requirements. In apreferred embodiment, network equipment building standards (NEBS) level3 is satisfied.

Because ATM is a packet oriented rather than circuit orientedtechnology, ATM must emulate circuit characteristics in order to carryconstant bit rate (CBR) traffic such as voice. This emulation isreferred to as a circuit emulation service (CES). The T-IWF 28 convertsbetween the 64 Kbps trunks and ATM cells by employing a well knownmethod of circuit emulation that is described in “Circuit EmulationService Interoperability Specification Version 2.0” by The ATM ForumTechnical Committee (January 1997), which is expressly incorporatedherein by reference in its entirety. Preferably, the structured digitalservice level 1 (DS1) n×64 Kbps service described in the CESinteroperating specification is employed to connect DS1 equipment acrossemulated circuits carried on an ATM network. The structured DS1 n×64Kbps circuit emulation system efficiently carries TDM trunks through theATM trunking network. The structured DS1 CES requires ATM switches totreat one or more DS0s in a T1 circuit as individual ATM virtualconnections.

According to the structured DS1 CES service, each interworking functionis connected to an ATM network 26 via physical interfaces. The physicalinterfaces are ATM user network interface (UNI) physical interfaces thathave two characteristics or requirements. The first requirement is thatthe ATM interface provides adequate bandwidth to carry n×64 trafficafter segmentation. The second requirement is that the ATM interfacemust be able to convey timing traceable to a primary reference sourcefrom the ATM network to the interworking function when externalconnection to network timing is not supported. The interworkingfunctions are also connected to standard constant bit rate (CBR)circuits, such as end offices 20, 22. Connected in this manner, theinterworking functions extend the constant bit rate (CBR) circuit acrossthe ATM network 26 in a manner transparent to the switches 20, 22.

An important function of the circuit emulation service operating withinthe T-IWF 28 is the adaptation of circuit traffic to ATM cells. Thisfunction is called the ATM adaptation. As described above, when timedivision multiplexed trunks are converted to ATM cells, the ATMadaptation process occurs. More generally, ATM adaptation refers toconverting non-ATM formatted information into the size and format of ATMcells. For circuit traffic such as voice to be converted into ATMformat, two adaptation layers that can be suitably used are ATMadaptation layer 1 (AAL1) and ATM adaptation layer 2 (AAL2). However,the present invention is not limited to AAL1 and AAL2 and other layersthat can satisfactorily convert the traffic into ATM cells, such asAAL5, may be employed.

According to one preferred embodiment, the structured DS1 n×64 Kbpscircuit emulation service employs AAL1 such that circuit traffic istreated as constant bit rate (CBR) traffic within the ATM tandemswitching system. However, the system is not limited to AAL1 and otherprotocols such as AAL2 may be adopted to incorporate bandwidth savingfeatures such as voice compression and silence suppression, which canfurther improve bandwidth efficiency.

AAL1 has been standardized in both International TelecommunicationsUnion Telecommunication (ITU-T) and American National StandardsInstitute (ANSI) since 1993 and is preferred for use with circuitemulation services due to its simplicity. AAL1 is designed to supportconstant bit rate services and allows the specification of peak cellrate, cell loss ratio, and cell delay variation. Depending onimplementation, the peak cell rate bandwidth may be dedicated orguaranteed.

There is a difference between dedicated and guaranteed bandwidth. Whenthe peak cell rate bandwidth is said to be dedicated to the constant bitrate service, no other services can utilize any of the constant bitrate's bandwidth, even if it is not utilized by the constant bit rateservice itself. However, if the peak cell rate bandwidth is guaranteedto the constant bit rate service, the unused portion of the constant bitrate's dedicated bandwidth can be utilized by other services, so long asthe other services agree to return the bandwidth when the constant bitrate service needs it.

AAL1 introduces additional delay because each AAL1 ATM connectioncarries information for only a single user. With voice input at 64 Kbps,it takes 5.875 milliseconds, or approximately six milliseconds to fillan AAL1 payload of an ATM cell.

One alternative to AAL1 is AAL2. AAL2 started as a contribution tocommittee T1S1.5, an ANSI standards subcommittee. AAL2 was laterintroduced to the ITU-T Study Group 13 on May, 1996 under the temporaryname of AAL-CU where CU stood for composite user. AAL2 has now beendefined in the ITU-T Recommendation I363.2.

AAL2 enables voice to be carried as variable bit rate (VBR) data whilemaintaining its delay sensitive nature. AAL2's support for variable bitrate (VBR) traffic allows many bandwidth saving features, such as voicecompression and silence suppression to be employed. These features arediscussed in more detail below.

AAL2 enables multiple users to share a single ATM connection, whileallowing each user to select a potentially different quality of serviceparameter. The structure of AAL2 also allows for the packing of shortlength packets into one or more ATM cells. In contrast to AAL1, whichhas a fixed payload size, AAL2 offers a variable payload within cellsand across cells. The variable payload provides a dramatic improvementin bandwidth efficiency of the structured circuit emulation over AAL1.

An important aspect of AAL2 is the packet fill delay parameter. Thepacket fill delay parameter allows the network operator to set a timeperiod during which AAL2 protocol data units are assembled and thensegmented into ATM cells. The setting of this parameter allows thenetwork operator to control the cell construction delay. This allows theoperator to trade off delay and bandwidth efficiency in order to meetthe delay requirements of some voice connections. For example, for 64Kbps pulse code modulation (PCM) voice to fill up an ATM cell, it takessix milliseconds. AAL2 can reduce this delay by half by setting thepacket fill delay to 3 milliseconds, which would result in each ATM cellpayload being half filled. Thus, 50% bandwidth loss is traded for 50%less delay.

Essentially what AAL1 or AAL2 allow is the choice of carrying voicetrunks through an ATM network as constant bit rate traffic or variablebit rate traffic. If voice is sent as constant bit rate traffic, thenATM Forum's structured DS1 n×64 Kbps circulation emulation service usingAAL1 is employed. If voice is sent as real time variable bit ratetraffic, then AAL2 as the ATM adaptation layer is employed, thus takingadvantage of the many efficiency and performance enhancing featuressupported by AAL2.

The ATM network 26 will now be discussed. From a physical connectionpoint of view, the ATM trunks between switching offices may be setupwith direct point-to-point fibers or by means of a synchronous opticalnetwork (SONET) ring. However, logically ATM allows the interofficetrunks to be setup in many different ways. Thus, within the ATMswitching network 26, originating and terminating trunks are preferablyconnected by means of virtual connections setup in one of three ways.

According to a preferred embodiment of the invention, individualswitched virtual connections (SVC) are provided in which an ATM switchedvirtual connection is established for each n×64 Kbps call. Whenutilizing individual switched virtual connections, the switched virtualconnections are dynamically provisioned via signaling and a peak cellrate is set equal to n×64 Kbps. Available ATM network bandwidth thatwould otherwise be dedicated to carrying voice traffic can be utilizedby other data applications on a dynamic basis. Individual switchedvirtual connections have the advantage that they are automaticallysetup, and on demand provisioning results in trunk bandwidth efficiency.

According to another embodiment, a mesh permanent virtual path (PVP) isprovided. The mesh permanent virtual path establishes an ATM permanentvirtual path across the ATM tandem network between every two endoffices. Thus, the permanent virtual paths are manually provisioned witha peak cell rate equal to the size of the existing trunk group betweenthe two end offices. As with individual switched virtual connections,available ATM network bandwidth that would otherwise be dedicated tocarrying voice traffic can be utilized by other data applications on adynamic basis. Among, the advantages of the mesh permanent virtual pathare that little or no signaling is required depending upon how manyvirtual connections are used within the permanent virtual paths. Thatis, all that is required is getting allocated within a path; no setup isrequired. In addition, every end office perceives direct trunks withevery other end office. However, the mesh permanent virtual pathrequires manual provisioning and the preallocated and guaranteedconstant bit rate bandwidth reduces trunk bandwidth efficiency.

According to yet another embodiment, a star permanent virtual path isprovided. With a star permanent virtual path, a single ATM permanentvirtual path is established between each end office and the ATM tandemnetwork. The permanent virtual path is manually provisioned such thatonly one permanent virtual path is provisioned and a peak cell rate isset equal to the sum of all the trunks of the end office. As with theother two systems, available ATM network bandwidth that would otherwisebe dedicated to carrying voice traffic can be utilized by other dataapplications on a dynamic basis. Similar to the mesh permanent virtualpath, the star permanent virtual path has the advantage of little or nosignaling, depending on if and how virtual connections are used in thepermanent virtual path. Moreover, each end office perceives a singletandem trunk. In addition, switch translation is easy because it appearsthat a single trunk leaves each end office. Thus, all traffic isdirected to that trunk group. However, the star permanent virtual pathhas the drawbacks of manual provisioning, and preallocated andguaranteed constant bit rate bandwidth reduces trunk bandwidthefficiency.

The star permanent virtual path and the mesh permanent virtual pathremove the majority of the call setup load from the switch by utilizingmanually provisioned permanent virtual paths. Utilizing the individualswitched virtual connection increases call setup load due to theelimination of direct trunks. That is, calls previously using directtrunks will now traverse to the ATM tandem switch.

The function of the CS-IWF 30 is to bridge between narrowband signalingin the PSTN and broadband signaling within the ATM network 26. Two typesof interoffice signaling methods are employed in present day networks,common channel signaling (CCS) (i.e., narrowband signaling) and channelassociated signaling (CAS). CAS is an older kind of signaling in whichsignaling information is carried in the same bearer channel as the userinformation and is of little concern to the present invention.

Because the dominant interoffice signaling protocol currently in use isSignaling System 7 (SS7), the CS-IWF 30 is provided for interacting withSS7 and enabling support of SS7 within the ATM network 26. SS7 is acommon channel signal (CCS) protocol for call control information. Theprotocol is transported via a physically separate network from that ofthe voice bearer channels.

With reference to FIG. 5, explanation is provided as to how the presentinvention supports the SS7 signaling within the ATM network 26 bypreserving the existing SS7 signaling process and the ISUP messageintegrity. The originating end office 20 sends its ISUP message to thesignaling transfer point 18 as described above. Subsequently, thesignaling transfer point 18 forwards the message to the CS-IWF 30, whichtranslates incoming ISUP messages into ATM signaling messages. Forexample, the unique point codes are translated into ATM addresses. AnATM connection is then established between the two T-IWFs 28 via an ATMsignaling protocol such as broadband-ISDN user part (B-ISUP) defined bythe ITU-T, PNNI defined by the ATM Forum, or UNI 3.0, 3.1, 4.0 definedby the ATM Forum. On the destination side, the T-IWF 28 composes an ISUPmessage and sends it to the signaling transfer point 18, which thencompletes the connection setup with ISUP messages to the destination endoffice 22.

An exemplary call flow according to the present invention is nowdescribed with reference to FIG. 5. After the originating end officecreates an ISUP message, the originating end office sends the ISUPmessage to the signaling transfer point 18. The signaling transfer point18 routes the ISUP message to the CS-IWF 30 via a set of A-links(connections between the end office and the STP). At the CS-IWF 30, theISUP message is processed and call control information is distributed tothe T-IWFs 28 via the ATM network 26. The CS-IWF 30 also formulates anISUP message regarding the receiving trunk and sends it back to thesignaling transfer point 18. The signaling transfer point 18 routes theISUP message to the terminating end office 22. The terminating endoffice then reserves the corresponding trunk. At this point, an ATMvirtual connection can be established between the T-IWFs 28 to carry thevoice traffic. Thus, the CS-IWF 30 converts between narrowband and ATMsignaling to establish connections. The ATM virtual connections aredynamically setup by the system via signaling as described above withreference to the SVCs. Although the signaling protocols must bestandards based, such as ATM UNI or PNNI, the exact protocol may varyamong implementations.

Transporting the ISUP messages from the end offices 20, 22 can beaccomplished in two ways. The ISUP messages can be carried in the SS7network without change, or the ISUP messages can be carried in the ATMnetwork in a special ATM connection. According to a preferredembodiment, the ISUP messages are carried in the SS7 network because itsimplifies the IWF's responsibility and preserves the out of band natureof the SS7 signaling network.

The CS-IWF 30 should have a unique point code. For a system with aredundant pair of CS-IWFs, two point codes may be assigned. Two sets ofT1 interfaces to a mated pair of signaling transfer points should alsobe provided. In addition, an ATM OC-3 user to network interface (UNI) tothe ATM network should be provided. Preferably, the CS-IWF 30 currentlysupports a trunking network of at least 500,000 trunks and is able toconnect 3,000,000 calls in a busy hour. As new processors are developed,capacity will increase.

Preferably, the T-IWF 28 scales from less than 100 to 16,000 trunks.Similar to the CS-IWF 30, as new processors are developed, capacity willincrease. According to a preferred embodiment, the interface is T1, T3,and OC-3 compatible on the TDM end and DS-3, OC-3, and OC-12 on the ATMside. Preferably the ATM signals are UNI 3.1, UNI 4.0, or PNNI 1.0 onthe ATM side. Each call is carried by an ATM switch virtual connectionsetup via signaling. The T-IWF 28 is a multiplexer as opposed to aswitch. That is, the switching function is not within the T-IWF 28 forcost considerations.

From an implementation point of view, the T-IWF 28 and the CS-IWF 30 canbe separate (as described above in the preferred embodiment), orintegrated. If they are implemented as separate entities, one CS-IWF 30may serve one T-IWF 28, or the CS-IWF 30 may centrally serve multipleT-IWFs 28.

Multiple implementations are possible for the T-IWF 28. It may beintegrated into the switch 20, 22, may be integrated into an ATM edgeswitch, or may be provided as a stand-alone special purpose devicehaving no switching capability. Providing the T-IWF 28 within the ATMedge switch or as a stand-alone requires minimum or no change toexisting switches 20, 22. Preferably, the T-IWF 28 is closely co-locatedwith the switch 20, 22 in the same end office in order to maximizetrunking efficiency.

The CS-IWF 30 may be integrated into the switch 20, 22 or an ATM edgeswitch, or may be a stand-alone, special purpose device having noswitching capability. The CS-IWF 30 can also be integrated into thesignal transfer point 18. As shown in FIG. 7, if the CS-IWF 30 is partof the ATM edge switch, the ATM edge switch preferably operates as anintegrated IWF 40, i.e., containing both the T-IWF 28 and the CS-IWF 30.In this case because the CS-IWF 30 and the T-IWF 28 are physicallyintegrated into the ATM edge switch, they maintain a one-to-onerelationship. Preferably, the ATM edge switch is then co-located withthe switch in the end office. According to this embodiment, the CS-IWFs30 are seen as distributed to each end office.

According to an embodiment of the present invention, silence suppressionis employed. Silence suppression is a mechanism for saving extra networkbandwidth by not transmitting the pauses in a voice conversation intothe network. Silence suppression can be employed on the sender's end bynot generating voice samples when the speech level is below a threshold.With adaptive differential pulse code modulation (ADPCM) the silencesuppression results in fewer bits per sample during speech inactivity.Silence suppression can be performed in an ATM trunking network, forexample, by a voice module on an ATM edge switch. The voice moduledetects silence and stops the transmission of these silent intervalsinto the ATM network.

Silence suppression also suffers from side effects. For example, becausesilence suppression removes background noise, a listener may think thatthe line has been disconnected when a pause in the conversation occurs.Silence suppression also increases the ATM cell construction delay andadds variability to the delay. Silence suppression should always bedisabled when fax or modem tones are detected. For ATM trunking, thesilence suppression feature is not required, however, the availabilityof silence suppression does improve the network efficiency.

Voice compression is another way of saving network bandwidth. Voicecompression employs algorithms such as ADPCM to reduce standard PCM 64Kbps voice tone to 32 Kbps, 24 Kbps, 16 Kbps, or even 8 Kbps. However,the side effects of voice compression are degraded voice quality andincreased ATM cell construction delay. As with silence suppression,voice compression is not required but may be employed in an embodimentof the present invention.

ATM trunking for narrowband services introduces delay additional to thedelay caused by transport over the ATM network. The additional delay isprimarily associated with buffering to accommodate cell delay variationintroduced by the ATM network and cell construction delay. Thus, thethree types of delay that voice traffic may experience when carried byan ATM network are: ATM switch and network transit delay, bufferingdelay in the ATM switch to accommodate cell delay variation, and ATMcell construction delay. While the first two types of delay aredependent on switch design, physical medium, distance, and trafficcondition, etc., the ATM cell construction delay, when employing theAAL1 circuit emulation service, is fixed. As mentioned above, for 64Kbps pulse code modulated (PCM) voice, it takes six milliseconds to fillan ATM cell with a single voice channel. The total echo path time isthus 12 milliseconds plus additional transit and buffering delays. Forcompressed voice, for example 32 Kbps using ADPCM, the delay will bedoubled to 24 milliseconds because it now takes twice as long to fill anATM cell with the speech data of a single voice channel.

In order to counteract excessive delay, appropriate echo controlmeasures are employed on all speech connections where end delay issignificant. According to a preferred embodiment, an active echo controldevice is employed on all connections that exceed the total one way talkor echo transmission path of 25 milliseconds.

A call flow scenario according to the present invention is now describedwith reference to FIG. 6. Initially, a calling party 19, e.g., 235-1111dials a destination 23, e.g., 676-2222. The calling party's end office20 (end office A) collects the dialed digits corresponding to the callednumber and checks routing tables to determine the end office that isconnected to the dialed destination. After determining the destinationend office 22 (end office B), end office A finds a trunk (e.g., trunk 6)connecting to end office A=s T-IWF 28. Assuming that the trunk is idle,end office A reserves trunk 6.

End office A then initiates an SS7 IAM message containing, among otherinformation, the following: signaling transfer point routing address ofthe CS-IWF 30; calling telephone number; called telephone number; andtrunk identification (CIC) for trunk 6. After the signaling transferpoint 18 receives the IAM message, the signaling transfer point 18forwards the message to the CS-IWF 30. The CS-IWF 30, based on thecalling telephone number, identifies the originating T-IWF 28 (T-IWF A)with its ATM address or other identifier. The CS-IWF 30 then sends theCIC to T-IWF A via an ATM message through the ATM network (i.e., in-bandsignaling). The CS-IWF 30, based on the called telephone number,identifies the destination T-IWF 28 (T-IWF B) with its ATM address orother identifier. The CS-IWF 30 then sends a request to T-IWF B for anidle trunk, via an ATM connection (i.e., inband signaling) in the ATMnetwork 26.

T-IWF A receives the message from the CS-IWF 30 and based on thereceived CIC, determines the corresponding DS0 channel on its lineinterfaces. T-IWF B also receives a request from the CS-IWF 30.Accordingly, T-IWF B finds an idle DS0 channel on its line interfacesand reserves it, e.g., trunk 35. T-IWF B determines the CIC for this DS0and sends the CIC to the CS-IWF 30 via an ATM message.

The CS-IWF 30 receives the message from T-IWF B and sends an IAM messageto the signaling transfer point 18 containing, among other information,the following: signaling transfer point routing address of end office B;calling telephone number; called telephone number; and trunkidentification (CIC). The signaling transfer point 18 receives the IAMmessage and forwards it to end office B.

End office B receives the IAM message and uses the received CIC toreserve the corresponding trunk, trunk 35. End office B checks thecalled telephone number for on-hook and active call features. End officeB holds the line, applies ringing to the line and a ring tone to trunk35 (assuming that 676-2222 is on-hook). End office B then connects theline to trunk 35 and initiates an SS7 ACM message to the signalingtransfer point 18.

The signaling transfer point 18 receives the ACM message and forwards itto the CS-IWF 30. When the CS-IWF 30 receives the ACM message, theCS-IWF 30 sends the message to T-IWF A, requesting that T-IWF Aestablishes an ATM connection with T-IWF B or vice versa. That is, T-IWFB can establish a connection with T-IWF A.

In response to the received message, T-IWF A establishes a 64 Kbps CBRconnection with T-IWF B. T-IWF A also maps the appropriate DS0 to theoutgoing switched virtual connection. At the same time, T-IWF Bassociates the incoming switched virtual connection to the correspondingDS0. After the connection is established, T-IWF A sends an ATM messageto the CS-IWF 30, indicating the establishment of the ATM connection.

The CS-IWF 30 receives the message from T-IWF A and the CS-IWF 30 sendsan ACM message to the signaling transfer point 18. The signalingtransfer point 18 receives the ACM message and forwards it to end officeA. End office A receives the ACM message from the signaling transferpoint 18 and connects 235-1111 to trunk 6.

Consequently, the calling party 19 at 235-1111 hears the ringing tone.When the destination 23 at 676-2222 picks up the phone, end office Bdetects the off-hook and removes the ringing tone. End office B theninitiates an ANM message to the signaling transfer point 18. Thesignaling transfer point 18 receives the ANM message and forwards it tothe CS-IWF 30. The CS-IWF 30 receives the ANM message from the signalingtransfer point 18 and initiates an ANM message to the signaling transferpoint 18.

The signaling transfer point 18 receives the ANM message from the CS-IWF30, and forwards it to end office A. End office A receives the ANMmessage from the signaling transfer point 18 and starts necessarybilling measurement. Finally, the calling party 19 at 235-1111 talks tothe destination 23 at 676-2222.

The present invention thus allows for savings in three broad categories:end office trunk termination reduction and/or growth offsets, bandwidthreduction on transport facilities associated with end office trunktermination reduction, and administrative savings associated with trunkforecasting and trunk record keeping.

The use of large trunk groups according to the present invention createsan increased carrying capacity that results in a reduction in end officetrunk unit requirements. The reduction allows for a decrease in capitaloutlays for trunk units and/or allows for more rapid response to theincreasing trunk requirements brought about by new traffic such asInternet access traffic.

Bandwidth reduction on transport facilities also occurs because currentinteroffice trunks utilize bandwidth whether the trunk is in use or not.The present invention permits trunks to utilize bandwidth on transportfacilities only when the trunk is in use. When the trunk is idle, nobandwidth on the transport facility is required. During low trafficperiods such as late evenings and early mornings, available bandwidth onthe transport facilities could increase in excess of 50%. Consequently,the bandwidth is available for other applications, such as data or filetransfers.

Administrative savings are realized in two areas, trunk forecasting andtrunk record keeping. The nature of trunking today requires hugeinvestments in hardware and software for systems to keep track ofindividual interoffice trunks. The present invention negates the needfor such detailed record keeping by individual trunk because the trunksare virtual. Therefore, individual trunks spanning the network existonly when the calls are in progress. Consequently, keeping records onindividual interoffice trunks can be drastically reduced.

Trunk forecasting and provisioning for thousands of individual trunkgroups can be reduced to just a few trunk groups per end office. Callloads for the end office can be used to forecast trunk requirementsrather than individual trunk and trunk group measurements. Datacollection can also be simplified due to a reduction in the amount ofdata needed to accurately measure office carrying capacity loads.

According to another embodiment, the Class 5 feature set may residewithin the CS-IWF 30. Further, a switch management system may beprovided to manage all switch peripherals and do all OAM&P (operations,administration, maintenance, and provisioning) for the switch. Theswitch management system will do point-to-point private line setups.

The present invention has utility in many environments other than tandemswitching systems, such as a wireless environment and a digitalsubscriber line environment. For wireless services, a T-IWF can beplaced in the mobile switching center to convert the trunk traffic toATM traffic and send it to the ATM-based virtual tandem switch. TheT-IWF may operate with asymmetric digital subscriber lines (ADSL) byhosting the digital subscriber line access multiplexer (DSLAM) function.

The present invention also applies to Internet services providers. Thepresent invention facilitates a more efficient way of carrying dial upInternet connections. Currently, an Internet user typically accesses theInternet by connecting to the Internet service provider via a dial upmodem. That style of connection consumes resources in the PSTN networkjust like a regular voice connection. However, unlike a voiceconnection, a modem connection carries bursty data with InternetProtocol (IP) packets. It is wasteful for bursty data to be carried byTDM circuits. Thus, the T-IWF provides an ideal place to implement amodem pool that terminates the dial up connections and converts them toATM connections. These ATM connections can be carried by the ATM networkto the respective Internet service providers. Depending on the Internetservice provider's ability to receive ATM connections, these connectionsmay be delivered to the Internet service provider as ATM, or beconverted back to IP packets. The modem termination capability on theT-IWF helps make more efficient use of network resources by carryingInternet traffic as data traffic using ATM connections.

The present invention also applies to broad band advanced intelligentnetworks (AIN). The CS-IWF is an ideal place for broad band advancedintelligent network capabilities to reside. Keeping the CS-IWF as acentral point of intelligence with an open interface allows new servicesand capabilities to be developed and deployed in the entire network veryquickly.

The present invention also has applicability in provisioning leasedprivate lines (i.e., High Cap circuits). Provisioning leased privatelines in today's network is a complicated and error prone process. Usingthe proposed ATM network, much of the complexity and provisioning can beeliminated, owing to ATM's capability of automatically setting upconnections via signaling. Only the tail circuits at the end points needto be manually provisioned and maintained.

Interexchange carrier networks may also take advantage of the presentinvention. For end offices having trunks to an interexchange carrier(IXC) network, the IXC trunks remain time division multiplexed andunchanged. End offices not having direct trunks to the interexchangecarrier network can choose to utilize either the time divisionmultiplexed tandem network or the ATM band system to carry their trafficto the interexchange carriers. If the interexchange carrier trunks arecarried by the ATM tandem network, a T-IWF will need to be placed at theinterface between the local exchange carrier and the interexchangecarrier networks to act as a gateway. For the ATM-based system, asimilar T-IWF is provided at the interface between the local exchangecarrier and the interexchange carrier network to act as a gateway.Further, the T-IWF may be provided with the ability to terminate trunksfrom an interexchange carrier. The T-IWF also ensures that billing isdone correctly. This arrangement applies not only to interexchangecarrier switches, but also to switches owned and operated by independentlocal telephone service providers or competitive local exchangecarriers.

Although the invention has been described with reference to severalexemplary embodiments, it is understood that the words that have beenused are words of description and illustration, rather than words oflimitation. Changes may be made within the purview of the appendedclaims, as presently stated and as amended, without departing from thescope and spirit of the invention in its aspects. Although the inventionhas been described with reference to particular means, materials andembodiments, the invention is not intended to be limited to theparticulars disclosed; rather, the invention extends to all functionallyequivalent structures, methods, and uses such as are within the scope ofthe appended claims.

1. A control system for transporting voice over a packet network,comprising: a centralized control and signaling interworking function(CS-IWF) device centrally serving a plurality of gateways, the CS-IWFdevice performing call control functions, providing a single connectionbetween a narrowband signaling network and the packet network,interfacing narrowband and broadband signaling for call control withinthe packet network so that telephone calls originating and/orterminating within a public switched telephone network are transmittedthrough the packet network, and communicating with the plurality ofgateways via the packet network to send call setup information.
 2. Thecontrol system of claim 1, in which the narrowband signaling comprisesSS7 signaling.
 3. The control system of claim 2, in which the SS7signaling comprises ISDN user part (ISUP) messages.
 4. The controlsystem of claim 1, in which the gateways operates with digitalsubscriber lines (DSL).
 5. The control system of claim 1, in which thegateways receives internet protocol (IP) traffic.
 6. The control systemof claim 1, in which the CS-IWF further comprises a Class 5 feature set.7. The control system of claim 1, wherein the CS-IWF device facilitatesdynamically setting up switched virtual connections within the packetnetwork.
 8. A method for transporting voice across a data network, themethod comprising: receiving narrowband call processing signaling;converting between the narrowband call processing signaling andbroadband call processing signaling; and forwarding the broadband callprocessing signaling, via the data network, to at least one gateway sothat telephone calls originating and/or terminating within a publicswitched telephone network are transmitted through the at least onegateway and the data network.
 9. The method of claim 8, in which thenarrowband signaling comprises SS7 signaling.
 10. The method of claim 8,in which the at least one gateway receives data via digital subscriberlines (DSL).
 11. The method of claim 8, in which the at least onegateway receives internet protocol (IP) traffic.
 12. The method of claim8, further comprising providing Class 5 features.
 13. The method ofclaim 8, in which the forwarding further comprises instructing dynamicsetting up of switched virtual connections within the data network. 14.A computer readable medium storing a program for transporting voiceacross a packet network, comprising: a receiving code segment thatreceives narrowband call processing signaling; a converting code segmentthat converts the narrowband call processing signaling to broadband callprocessing signaling; and a call management information forwarding codesegment that forwards the broadband call processing signaling to atleast one gateway via the packet network so that telephone callsoriginating and/or terminating within a public switched telephonenetwork are transmitted through the packet network.
 15. The computerreadable medium of claim 14, in which the narrowband signaling comprisesSS7 signaling.
 16. The computer readable medium of claim 15, in whichthe SS7 signaling comprises ISDN user part (ISUP) messages.
 17. Thecomputer readable medium of claim 14, further comprising a digitalsubscriber line (DSL) code segment that receives data via DSL.
 18. Thecomputer readable medium of claim 14, further comprising an internetprotocol (IP) code segment that receives IP traffic.
 19. The computerreadable medium of claim 14, further comprising a Class 5 feature codesegment that offers Class 5 features.
 20. The computer readable mediumof claim 14, further comprising a switched virtual connection codesegment that dynamically sets up an individual switched virtualconnection across the packet network.